Sports boot in very stiff material

ABSTRACT

Sports boot subassembly of the shell or collar type, which comprises at least two parts, each comprising a flexible plastics material injection-overmolded over a very stiff material partially embedded in the flexible plastics material, and wherein the at least two parts comprise an assembly surface for joining them together.

BACKGROUND OF THE INVENTION

The invention relates to a sports boot subassembly and also to the sports boot itself, and is particularly suited to the field of boots for boards for gliding, such as skiing or snowboarding, or skating boots, which are subjected to significant stresses during use and for which a particularly robust structure is required. For example, the invention relates to subassemblies of the shell or collar type for a ski boot. The invention also relates to a manufacturing process.

A ski boot is a good example of a boot subjected to numerous stresses that has to be very stiff. However, it also has to be sufficiently flexible to guarantee the skier's comfort and to enable him to open the boot in order to put it on and to take it off and to enable him to flex his knees forward.

DESCRIPTION OF THE PRIOR ART

A process for manufacturing a ski boot was described in patent EP 1295540, allowing the production of a ski boot with the aid of several carbon-fiber fabrics connected by a resin by means of a technique of polymerization of the resin on molds in order to form two half-shells, prior to the joining of the two half-shells in order, finally, to form the boot. This process makes it possible to obtain a very stiff boot but has a first disadvantage of being complex and costly compared to currently used injection-molding techniques, such an injection-molding operation not being applicable in the case of a reinforced material, a second disadvantage of not meeting the requirements of flexibility of such boots, and a third disadvantage of allowing only a basic design for the outer surface of the boot. For these reasons it was quickly abandoned.

In response to the disadvantages mentioned above, the processes for manufacturing ski boots that are most in use nowadays are based on processes of injection-molding of plastics materials of polyurethane, polypropylene, polyethylene or polyamide type. Such a solution is described in patent application EP 0903087, which discloses a boot shell composed of a first layer in a relatively stiff plastics material of polyurethane type partially covered by a second layer in a more flexible plastics material, the relatively stiff layer including thicker zones in order to form reinforcements on certain carefully selected surfaces. A first disadvantage of this solution is that it greatly increases the overall weight of the boot on account of the weight of the materials used and their considerable total thickness. A second disadvantage stems from the fact that the performance levels obtained in terms of stiffness are mediocre, despite the various increased thicknesses used. A third disadvantage stems from the fact that such boots are ill-suited to the production of adornments on their outer surfaces. Indeed, the adornment of the outer surface may either be achieved with the aid of specific shapes given to the plastics material placed on the outer surface of the boot, which gives rise to increased thicknesses of plastics for the production of designs, these increased thicknesses generating excess weight and an increase in the boot's stiffness, and thus, ultimately, having a negative impact on the essential characteristics of the boot, or be produced with the aid of marks on the outer surface of the boot, such marks generally lasting only a short time given the numerous aggressive influences to which they are subjected.

SUMMARY OF THE INVENTION

An object of the present invention consists in proposing a sports boot subassembly and a process for manufacturing it that does not present the disadvantages of the prior art.

More precisely, a first object of the present invention consists in proposing a sports boot subassembly that makes it possible to achieve satisfactory stiffness while conserving zones of flexibility.

A second object of the present invention consists in proposing a sports boot subassembly that is light in weight.

A third object of the present invention consists in proposing a sports boot subassembly that has an attractive esthetic appearance.

A fourth object of the present invention consists in proposing a process for manufacturing a sports boot subassembly that is relatively simple.

According to the concept of the invention, the wall of a sports boot subassembly astutely combines the use of a very stiff material and a flexible plastics material in such a way as to achieve a good stiffness/flexibility compromise for minimum weight. This combination of materials is, furthermore, defined in order to allow implementation of a simple manufacturing process.

More precisely, the invention relates to a sports boot subassembly of the shell or collar type, which comprises at least two parts, each comprising a flexible plastics material and a very stiff material partially embedded in the flexible plastics material, and wherein the at least two parts comprise an assembly surface for joining them together.

Advantageously, the very stiff material occupies at least half the total surface area of the wall of the subassembly.

The invention also relates specifically to a ski boot shell and to a ski boot.

It also relates to a process for manufacturing a sports boot subassembly of the shell or collar type, wherein it is obtained by the assembly of several parts, at least two of these parts being obtained by means of the following steps:

-   -   production of a blank in very stiff material;     -   injection-overmolding of a flexible plastics material over the         very stiff material, linking the very stiff material to the         injection-molded flexible plastics material, in order to form         part of the sports boot subassembly.

The blank in very stiff material may be obtained from a composite sheet composed of a fiber-reinforced thermoplastic or thermosetting matrix or by means of drawing a metal sheet.

DESCRIPTION OF THE DRAWINGS

These objects, characteristics and advantages of the present invention will be set forth in detail in the following description of a non-limiting particular embodiment with reference to the appended figures, in which:

FIG. 1 shows a side view of the outer face of a first part of a ski boot shell according to the invention;

FIG. 2 shows a sectional view on the axis II, of the first part of the ski boot shell of FIG. 1;

FIG. 3 shows a side view of the inner face of the first part of the ski boot shell of FIG. 1;

FIG. 4 is a bottom view of the two parts of the ski boot shell according to the invention, prior to their assembly.

FIGS. 1 to 4 illustrate an embodiment of the invention for manufacturing a ski boot shell.

FIGS. 1 to 3 illustrate a first part 1 of a ski boot shell according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

This part 1 has a wall composed of a very stiff material 2 and a flexible plastics material 3. In this embodiment, the very stiff material is a reinforced material composed of a carbon-fiber-reinforced polyurethane thermoplastic matrix and the flexible plastics material is a polyurethane of 55 Shore D hardness.

As shown in FIG. 1, the outer surface of the wall of the first part 1 comprises a zone 4 in which the reinforced material 2 is not covered and forms the outer surface directly in contact with the outside of the wall, a zone 5 in which the reinforced material is covered by the plastics material, principally as a thin layer, and a zone 6 beyond the periphery 7 of the blank in reinforced material 2 indicated by a dotted line where the wall comprises only plastics material 3. Increased thicknesses 8 in plastics material are produced on the outer surface of the part 1 with a view to reinforcing the zones serving as pole deflectors, for example, to form the rear and front curbs and also to produced special designs in order to create an attractive esthetic effect. Furthermore, the plastics material is used in a thinner thickness in order to form a flexible flap 9 over the instep and a flexible upper part 10 at the shin, in the above-mentioned zone 6.

As illustrated in FIG. 2, the blank in reinforced material 2 is thin and is also incorporated into the sole 11 of the shell.

FIG. 3 illustrates a view of the inner face of the wall of the part 1, i.e. that face that will be in contact with a user's foot in the finished shell. This face comprises a first zone where the wall is composed of the reinforced material 2 covered by a thin layer of plastics material 3, this zone corresponding to the zones 4 and 5 defined previously on the outer face, and a second zone in which the wall is composed only of plastics material, which corresponds to the zone 6 defined previously. The function of the thin layer of plastics material which covers the reinforced material 2 is to thermally insulate the inside of the shell—a thin layer thus suffices. A part of the periphery of the part 1 defines an assembly surface 12 designed to be connected to the assembly surface of a corresponding part, as will be described in connection with FIG. 4, which has a rib 13 running along its entire length. This assembly surface is composed of the plastics material 3, the reinforced material 2 coming to within a few millimeters of it. The zone 5 on the periphery of the blank in reinforced material 2, over which the reinforced material is embedded in the plastics material, i.e. sandwiched by the plastics material, helps to produce a mechanical link between the two materials. Openings 14 are, furthermore, present in the reinforced material 2 in this zone 5, and these are filled with the plastics material 3. These openings 14 have the primary function of producing a mechanical link between the two materials and a secondary function of predefining attachment points for future accessories to be fixed onto the shell. This avoids having to perforate the reinforced material, which could make it more fragile, giving rise to fiber rupture and cracks.

FIG. 4 illustrates a bottom view of two complementary parts 1, 21 of a boot shell just prior to their assembly, which consists in joining their two assembly surfaces 12 and 22 by incorporating the rib 13 of the part 1 into the corresponding groove 23 of the part 21. Assembly is then finalized by welding, bonding or any other equivalent assembly process. This link based on a rib 13 makes it possible to ensure satisfactory stiffness and mechanical strength and also provides a good seal at the link. Linking elements 24 are fixed under the sole in order to further reinforce the fixing of the two parts 1 and 21. The part 21 is not illustrated in detail as it has a wall that is very similar to the part 1.

Lastly, the shell obtained includes a reinforced material 2 that is present over more than half the total surface area of its wall. Furthermore, except for the zones of the periphery of the blanks in reinforced material 2 and the reinforcement zones 8, the wall of the shell comprising the reinforced material is very thin as it comprises the thickness of the reinforced material, optionally covered by a thin layer of plastics material. The shell is composed of two distinguishable parts 1, 21 connected by a fixing means that leaves an assembly line visible on the assembly surfaces 12 and 22.

The invention also relates to the process for manufacturing such a ski boot shell, which thus comprises the following steps:

-   -   production of a blank in reinforced material 2 by thermoforming         a reinforced thermoplastic matrix;     -   injection-overmolding a plastics material 3 in order to form a         first part 1 of the shell;     -   repeating the above two steps in order to form the second part         21 of the shell;     -   assembling the two parts.

The reinforced material may consist of a polyurethane matrix comprising carbon or glass fibers, and the plastics material may be polyurethane. According to another solution, allowing optimum recycling of the boot, the reinforced material may consist of polypropylene fibers embedded in a polypropylene matrix, the plastics material also being polypropylene. The fibers may, according to the applications and characteristics sought, be glass, carbon, Kevlar or polypropylene fibers.

As variant embodiments, the blank may be produced by last-molding a fiber-reinforced thermosetting matrix or by drawing a metal sheet. This blank may also include reinforcement ribs on its surface.

The injection-overmolding step may make it possible to form the top part of a shell comprising a flap 9 and a part 10 designed to bear on the shin and also reinforcements and/or front and rear curbs 8, the assembly surface 12 with the rib 13 and, possibly, shapes of an esthetic nature.

As a variant embodiment, the injection-overmolding step may comprise two successive steps of injection-molding a different plastics material, for example, allowing the injection-molding of a polyurethane of 65 Shore D hardness in order to form the front and rear curbs of the interface with the ski binding, and the injection-molding of a more flexible polyurethane of 45 Shore D hardness in order to form the flaps. The second injection-molding operation may also consist in the injection-molding of a cellular plastics material over the inner surface of the boot in order to exploit the comfort and thermal insulation properties thereof. Assembly may be achieved by any other solution—welding, bonding or mechanical fixing.

The invention has been described in the case of a ski boot shell, but it could be applied to the collar of a ski boot or to a subassembly of another sports boot.

In the embodiment described previously, the two parts of the shell correspond to two parts obtained by cutting the shell on a vertical plane passing through the center of the front and rear curbs. However, any other cutting plane could be imagined. The two complementary parts could also be designed in accordance with a non-planar cut, the assembly surfaces not being planar. Lastly, the concept of the invention could also be applied to the assembly of more than two parts of a boot subassembly.

The concept of the invention thus consists of the association of a very stiff material with a much more flexible injection-overmolded plastics material, which we will therefore call a flexible plastics material, the term flexible being understood to include any plastics material of which the flexibility is equivalent to that of a polyurethane customarily used for boots, whose hardness is between 30 and 70 Shore D, the expression “very stiff” being understood to be a material of markedly greater stiffness than the flexible plastics materials defined previously. The very stiff material may be any fiber-reinforced thermoplastic or thermosetting matrix or any metallic material, such as stainless steel, aluminum or magnesium. Its function is to ensure the stiffness of the boot by its very nature and to guarantee a light weight since it is, by nature, light and a thin layer suffices. The injection-overmolded plastics material has the function of providing flexibility in predetermined zones and forming the more complex decorative and functional parts of the boot, while fixing the two materials.

The embodiment described previously demonstrates an advantageous combination of a very rigid material with a flexible plastics material to form a wall of a sports boot. This combination could, however, be different without departing from the scope of the invention.

The flexible plastics material could also totally cover the very stiff material on the outer face, for example, with the aim of protecting a decoration arranged on the surface of the very stiff material and visible from the outside by using a transparent plastics material. The blank in very stiff material could also be arranged in the front and/or rear curbs of the shell. Lastly, the invention relates to any other combination of the very stiff material and the flexible plastics material in accordance with the concept explained above allowing the following objectives to be achieved.

-   -   a very stiff boot wall and reduced weight. To that end the blank         in very stiff material has to occupy a significant surface area         of the wall of the boot since it affords stiffness and reduced         weight. This surface area is regarded as large if it is more         than half the total surface area of the wall of the boot;     -   a boot wall having flexible zones and a reduced weight. To that         end, the plastics material has to occupy all zones of the boot         requiring flexibility and the total amount present on the other         zones where the very stiff material is located must be small or         zero. Thus, over the large surface area occupied by the blank in         very stiff material, the weight of the plastics material present         is markedly less than that customarily needed for prior-art         plastics boots;     -   the manufacturing process must be simple. To that end, the very         stiff material is chosen in accordance with a blank of a shape         that is relatively simple to manufacture, and the process of         injection-molding the plastics material is used to form the more         complex shapes of the wall of the boot. In particular, this         plastics material may form a design on the outer surface of the         boot. This design gives rise to an acceptable increase in         weight, since the boot is lighter overall and its impact on the         stiffness is negligible since the stiffness of the boot is         principally determined by the blank in very stiff material.         Thus, this boot is well suited to the production of a design         with the aid of special shapes produced in plastics material on         its outer surface. It is also well suited to a decoration         produced by marks, since such marks may be arranged on the blank         in very stiff material and be covered and protected by an         injection-overmolded transparent plastics material.

Finally, the advantages of the solution are thus as follows:

-   -   great stiffness, while conserving a satisfactory compromise         between the stiffness and the flexibility required in certain         zones, a low weight, as explained above;     -   a decoration that can easily be produced without involving major         modifications to the functional properties of the boot;     -   a simple manufacturing process. 

1. A process for manufacturing a sports boot subassembly of the shell or collar type, wherein it is obtained by the assembly of several parts, at least two of these parts being obtained by means of the following steps: production of a blank in very stiff material (2); injection-overmolding of a flexible plastics material (3) over the very stiff material, linking the very stiff material to the injection-molded flexible plastics material, in order to form part of the sports boot subassembly:
 2. The process for manufacturing a sports boot subassembly of the shell or collar type as claimed in claim 1, wherein the step of producing a blank in very stiff material (2) comprises a step of thermoforming a composite sheet composed of a fiber-reinforced thermoplastic matrix.
 3. The process for manufacturing a sports boot subassembly of the shell or collar type as claimed in claim 1, wherein the step of producing a blank in very stiff material (2) comprises a step of last-molding a fiber-reinforced thermosetting matrix.
 4. The process for manufacturing a sports boot subassembly of the shell or collar type as claimed in claim 1, wherein the step of producing a blank in very stiff material (2) comprises a step of drawing a metal sheet.
 5. The process for manufacturing a sports boot subassembly as claimed claim 1, wherein the injection-overmolding step comprises the injection of flexible plastics material on either side of the blank in very stiff material, at least over certain zones of its surface.
 6. The process for manufacturing a sports boot subassembly as claimed in claim 5, wherein the injection-overmolding step comprises the injection-molding of flexible plastics material on either side of the blank in very stiff material, at least over certain zones of its periphery.
 7. The process for manufacturing a sports boot subassembly as claimed in claim 6, which comprises the step consisting in producing at least one hole in the blank in very stiff material and wherein the injection-molding step comprises the passage of the flexible plastics material through the hole in order to traverse the very stiff material and to produce a fixing between the very stiff material and the flexible plastics material.
 8. The process for manufacturing a sports boot subassembly as claimed in claim 1, wherein the injection-overmolding step comprises the injection-molding of a thin layer of flexible plastics material over the inner face of the very stiff material.
 9. The process for manufacturing a sports boot subassembly as claimed in claim 1, wherein the injection-overmolding step comprises two successive substeps of injection-molding different flexible plastics materials.
 10. The process for manufacturing a sports boot subassembly as claimed in claim 9, wherein one of the injection-molding substeps consists of the injection-molding of a cellular flexible plastics material over the inner face of the very stiff material.
 11. The process for manufacturing a sports boot subassembly as claimed in claim 1, wherein the injection-overmolding step comprises the production in flexible plastics material, on each of the at least two parts, of complementary assembly surfaces.
 12. The process for manufacturing a sports boot subassembly as claimed in claim 11, wherein the injection-overmolding step comprises the production of a rib in flexible plastics material on the assembly surface.
 13. The process for manufacturing a sports boot subassembly as claimed in claim 12, wherein the step of assembling two parts comprises the incorporation of a rib of a first part into a corresponding groove of a second part in order to join the two assembly surfaces of the corresponding parts.
 14. The process for manufacturing a sports boot subassembly as claimed in claim 1, wherein the step of assembling two parts comprises the fixing of holding elements on each part on either side of the assembly line.
 15. The process for manufacturing a sports boot subassembly as claimed claim 1, wherein a decorative element is arranged on the blank in very stiff material and wherein said decorative element is covered by an injection-overmolded transparent flexible plastics material.
 16. A sports boot subassembly of the shell or collar type, which comprises at least two parts, each comprising a flexible plastics material and a very stiff material partially embedded in the flexible plastics material, and wherein the at least two parts comprise an assembly surface for fixing them together.
 17. The sports boot subassembly as claimed in claim 16, wherein the very stiff material occupies at least half the total surface area of the wall of the subassembly.
 18. The sports boot subassembly as claimed in claim 16, wherein the flexible plastics material at least partially covers the two inner and outer surfaces of the periphery of the very stiff material.
 19. The sports boot subassembly as claimed in claim 18, wherein the very stiff material has at least one hole filled by the flexible plastics material.
 20. The sports boot subassembly as claimed in claim 16, wherein the very stiff material has a part of its outer surface not covered by flexible plastics material.
 21. The sports boot subassembly as claimed in claim 16, which comprises a part of the surface of its wall that comprises only flexible plastics material.
 22. The sports boot subassembly as claimed in claim 16, which comprises a decoration arranged on the outer surface of the very stiff material and at least partially covered by the transparent flexible plastics material.
 23. The sports boot subassembly as claimed in claim 16, wherein the very stiff material has reinforcement ribs on its outer face.
 24. The sports boot subassembly as claimed in claim 16, wherein the very stiff material is a fiber-reinforced plastics material or a metallic material.
 25. A ski boot shell as claimed in claim 16, which comprises two parts, wherein the flexible plastics material forms two flaps in its top part and wherein the inner surface of the shell is covered at least by a thin layer of flexible plastics material serving as thermal insulation.
 26. The ski boot shell as claimed in claim 25, wherein the flexible plastics material forms reinforcements on the outer surface of the wall.
 27. A ski boot, comprising a subassembly as claimed in claim
 16. 